1. Field of Invention
The present invention relates to systems and methods for measuring and monitoring physiological changes in a body. More particularly, the invention relates to systems and methods for measuring and monitoring intracorporeal leaks in a body.
2. Description of Related Art
Surgery involving the gastrointestinal tract is commonly performed for a variety of reasons. In many cases, gastrointestinal surgery involves the division of the gastrointestinal tract and removal of a segment of the gastrointestinal tract. When the gastrointestinal tract is divided and/or a segment of the gastrointestinal tract is removed, a subsequent re-connection is performed to restore gastrointestinal continuity using suture material, surgical stapling devices, and/or various reinforcing materials. This re-connection is referred to as a gastrointestinal anastomosis.
After gastrointestinal anastomosis operations, leakage of material from the gastrointestinal tract into surrounding tissues or body cavities through the gastrointestinal anastomosis may occur. Leakage may result in significant patient morbidity and mortality due to the fact that gastrointestinal contents generally contain bacteria while the body compartments surrounding the gastrointestinal tract are generally sterile and ill equipped to mount an appropriate immunologic defense against bacterial elements. Ultimately, the tissues of the gastrointestinal tract in the area of an anastomosis undergo regenerative processes that completely seal any areas of potential leakage. In the first few weeks after surgery, while these regenerative processes are occurring, the surgical procedure used to form the anastomosis is expected to establish enough temporary integrity of the gastrointestinal wall to prevent leakage of materials from the gastrointestinal tract into surrounding body compartments. Despite the efforts of surgeons, anastomotic leaks may occur while the tissues undergo regeneration during the first few weeks after surgery.
Gastrointestinal anastomotic leak may also be devastating when it occurs after surgery involving the esophagus or the stomach (i.e., upper gastrointestinal surgery) because leakage from these structures may extend into the chest and specifically into the mediastinum. The mediastinum is vulnerable to a bacteriologic infection, known as mediastinitis. Patients who develop mediastinitis demonstrate very high morbidity and mortality. The leak rate after gastric or esophageal surgery is generally reported to vary from 2-20% of patients. In one large study of 1348 patients who had undergone resection of the esophagus, anastomotic leaks occurred in 52 patients, or 3.9%, and anastomotic leak was associated with a 42.3% mortality rate. Huang, G. J. et al., Carcinoma of the Esophagus and Gastric Cardia, Berlin: Springer, 1984, p. 285. In another study of 400 patients who had undergone roux-en-Y gastric bypass operations for morbid obesity, 5.25% of patients developed anastomotic leaks leading to a roughly 10% mortality rate as well as a significantly prolonged hospital stay. Marshall, J. S. et al., “Roux-en-Y gastric bypass leak complications” Archives of Surgery, vol. 138, no. 5, May 2003, p. 520-3.
Early identification and treatment of upper gastrointestinal anastomotic leaks may diminish associated morbidity and mortality. Marshall, J. S. et al., “Roux-en-Y gastric bypass leak complications” Archives of Surgery, vol. 138, no. 5, May 2003, p. 520-3. Clinicians have proposed numerous methods of identifying anastomotic leak prior to the onset of catastrophic infection; however, no definitive diagnostic test currently exists to establish the presence of anastomotic leak after upper gastrointestinal surgery. Furthermore, surprisingly few studies have objectively examined the sensitivity and specificity of the methods of leak detection. A recent review article presented an examination of the literature concerning anastomotic leaks and concluded that “[t]here is no universally accepted definition of anastomotic leak at any site. The definitions and values used to measure anastomotic failure vary extensively and preclude accurate comparison of rates between studies and institutions,” Bruce et al., British Journal of Surgery, vol. 88, no. 9, September 2001, pp. 1157-68. The methods of leak detection currently in use, though based on the clinical experience of numerous physicians, are substantiated only by anecdotal data.
Currently, common methods to identify anastomotic leak are: high degree of clinical suspicion; basic clinical parameters exhibited by the patient; and radiographic studies employing upper gastrointestinal contrast agents. Some clinicians rely on clinical suspicion to arrive at the diagnosis of anastomotic leak. Patients at increased risk for anastomotic leak may include: patients who have had prolonged operative times, patients who have undergone repeat operations or operations in which a great deal of scar tissue was encountered during the surgery, patients who have undergone previous radiation to the operative region, and patients in whom a question may have arisen concerning of the quality of the surgical anastomosis due to technical concerns. Clinicians also tend to rely on basic clinical parameters to identify the early stages of a potentially looming catastrophic infection that could be associated with an anastomotic leak. Tachycardia, fever, hypotension, abdominal pain, low urine output, leukocytosis, or even a subjective impression of patient instability all may contribute to making the diagnosis of anastomotic leak. Ultimately, if an anastomotic leak is suspected, the clinician will usually turn to a radiologic study to confirm the presence of the leak prior to taking steps to treat it. Generally, an upper gastrointestinal contrast study is obtained; this involves a radio-opaque contrast material that is swallowed by the patient or otherwise introduced into the upper gastrointestinal tract followed by the performance of a plane radiograph. Computed tomography may be added to this study to help increase the likelihood of detecting a leak Heiken, J. P. et al., “CT evaluation after esophagogastrectomy” American Journal of Roentgenology, vol. 143, no. 3, September 1984, pp. 555-60. Many surgeons obtain a routine upper gastrointestinal contrast study between post-operative days 2 to 5 to rule out the presence of an anastomotic leak whether or not the patient manifests clinical evidence of a leak. However, the value of performing upper gastrointestinal contrast studies to identify anastomotic leak has been questioned due to the very low sensitivity and specificity of this study in detecting anastomotic leaks, with some clinicians relying on clinical data alone to make the diagnosis. Singh, R. et al., “Sensitivity and specificity of postoperative upper GI series following gastric bypass” Obesity Surgery, vol. 13, no. 1, February 2003, pp. 73-5. Despite the lack of definitive data to defend the use of these methods, they continue to form the basis of current day anastomotic leak detection.
Other methods of diagnosing anastomotic leak have been reported in the medical literature but are not widely employed in clinical practice. One such technique involves the infusion of methylene blue dye into the upper gastrointestinal tract with its subsequent identification in drain effluent material confirmatory of an anastomotic leak. Ovnat, A. et al., “Early detection and treatment of a leaking gastrojejunostomy following gastric bypass” Israel Journal of Medical Sciences, vol. 22, no. 7-8, July-August 1986, pp. 556-8. This technique is employed intraoperatively by many surgeons, but is only rarely performed post-operatively to identify anastomotic leak. This pattern of use most likely results from the fact that the technique relies on the visual identification of blue dye extravasation. Intraoperatively, the placement of white towels around the anastomosis prior to infusion of methylene blue dye may improve the surgeon's ability to visually identify extravasated dye, but in the post-operative setting, the identification of blue dye in drain effluent, which may already be significantly discolored by blood or other materials, may be very difficult.
Other techniques that have been described include: measurement of the concentration of endotoxin in drain effluent from around the area of an anastomosis, Junger, W. et al., “Early detection of anastomotic leaks after colorectal surgery by measuring endotoxin in the drainage fluid” Hepato-Gastroenterology, vol. 43, no. 12, November-December 1996, pp. 1523-9; and the use of biliary scintigraphy, Herrlin, K., “The diagnosis of anastomotic leak after gastroesophagostomy with biliary scintigraphy” Clinical Nuclear Medicine, vol. 20, no. 8, August 1995, pp. 709-11. Currently, these methods are either rarely or never performed in clinical practice.
In summary, anastomotic leak is a major source of morbidity and mortality after upper gastrointestinal surgery that is most effectively treated when it is recognized early. However, no definitive diagnostic test for anastomotic leak exists at the current time and the sensitivity and specificity of the methods currently used have not been adequately determined. Moreover, in the medical literature, authors have pointed to the need for better definition of and identification of anastomotic leaks to improve the care of patients who undergo gastrointestinal surgery. Therefore, there is a recognized need for a device that would provide improved anastomotic leak detection.